Ban đầu: \(l_0;k_0\)
\(\dfrac{W_t}{W}=\dfrac{\dfrac{1}{2}kx^2}{\dfrac{1}{2}kA^2}=\dfrac{64}{100}=\dfrac{16}{25}\Rightarrow W_t=\dfrac{16}{25}W\)
\(W_d=\dfrac{1}{2}mv^2=\dfrac{9}{25}W\)
Lúc sau: \(l=\dfrac{3}{4}l_0;k=\dfrac{4}{3}k_0\)
\(\Rightarrow W_t'=\dfrac{3}{4}W_t=\dfrac{3}{4}.\dfrac{16}{25}W=\dfrac{12}{25}W\)
\(W_d'=W_d\)
\(\Rightarrow W'=W_t'+W_d'=\dfrac{12}{25}W+\dfrac{9}{25}W=\dfrac{21}{25}W=\dfrac{21}{25}.\dfrac{1}{2}.18.0,1^2=0,0756J=75,6mJ\)
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